[Boatanchors] SX25 Hallicrafters

[Richard Knoppow]

----- Original Message ----- 
From: "Joe Walden" <w5jdy at cox.net>
To: <boatanchors at mailman.qth.net>
Sent: Friday, March 07, 2014 11:04 AM
Subject: [Boatanchors] SX25 Hallicrafters


> From w5jdy in Norman,ok.....  I have an SX25 Halli that 
> has a defective
> audio output transformer...  I would like to find a 
> replacement for it but
> it has some odd speaker outputs..  It has a push pull 
> primary to match 6V6GT
> tubes and the output matches 5000 ohms and 500 ohms..  For 
> the 5000 ohms
> anything between 4000 and 10,000 would be ok and the 500 
> 0hms 600 ohms would
> be ok...   I would be happy with anything used or new to 
> match...  Joe w5jdy
> in Oklahoma..
> 405-321-4717

     The SX-25 has push pull 6F6 tubes but the transformer 
requirements are the same as for 6V6's.  For a long time 
Hallicrafters used a 5K output tap along with a 500 ohm tap. 
I think this was a hold over from the days when the output 
tranformer was in the loudspeaker cabinet. 5K was a typical 
one size fits all for many single-ended amplifiers. 
Speakers made with this sort of transformer could be 
connected to the 5K tap.  500 ohms was a standard for 
feeding phone lines for a long time and many speakers also 
had 500 ohm voice coils or matching transformers. For 
instance, many of the older Jensen speakers, at least up to 
the late 1940s had 500 ohm inputs.   For replacement 
purposes, if your desire is to get the set working rather 
than to restore it to complete originality, a transformer 
with the correct primary impedance and conventional low 
impedance speaker taps is quite suitable. The SX-25 does not 
take feedback off the secondary (or the primary either) so 
duplicating the original is not necessary for correct 
operation.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com